Ethylene vinyl acetate (EVA) is the predominant encapsulant in crystalline-silicon photovoltaic (PV) modules; however, its degradation is a subject of major concern, which causes significant power loss under field conditions. This article presents a comparison of EVA degradation in field-aged PV modules with glass/backsheet (G/B) and glass/glass (G/G) architectures. Module-level characterization included UV fluorescence imaging and I–V measurements. Material analytical techniques, including colorimetry, differential scanning calorimetry, thermogravimetric analysis, Fourier transform infrared spectroscopy, and Raman spectroscopy, were performed to correlate the module performance parameters with EVA material properties. An intense EVA discoloration in G/G modules was observed, which was corroborated by higher module $I_{sc}$ and Pmax degradation rates compared with its counterpart G/B modules. Higher power degradation was accompanied by a significant increase in EVA crosslinking, vinyl acetate content, yellowness index, and presence of functional groups containing unsaturated moieties that are linked to degradation products of photothermal reaction, and a higher decrease in the degree of crystallinity. The absence of a polymeric backsheet in hermetically sealed G/G modules, which restricts photobleaching and enhances the entrapment of volatile acetic acid and other degradation by-products, plays a major role in causing higher EVA degradation in G/G modules. This article concludes that EVA might have been a good choice of an encapsulant for the G/B modules over the decades, but it may prove to be an inappropriate choice for the G/G modules because of potential degassing, corrosion, and/or discoloration issues. Ionomers or polyester-based encapsulants like polyolefins could be best suited for G/G modules as it appears to be a current trend in the industry.

中文翻译：

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现场老化玻璃/背板和玻璃/玻璃光伏组件：密封剂降解比较

乙烯醋酸乙烯酯 (EVA) 是晶体硅光伏 (PV) 模块中的主要封装材料；然而，它的退化是一个主要关注的问题，在现场条件下会导致显着的功率损失。本文介绍了具有玻璃/背板 (G/B) 和玻璃/玻璃 (G/G) 架构的现场老化 PV 模块中 EVA 降解的比较。模块级表征包括紫外荧光成像和 I-V 测量。执行材料分析技术，包括比色法、差示扫描量热法、热重分析、傅里叶变换红外光谱和拉曼光谱，以将模块性能参数与 EVA 材料特性相关联。在 G/G 模块中观察到强烈的 EVA 变色，与其对应的 G/B 模块相比，更高的模块 $I_{sc}$ 和 Pmax 降解率证实了这一点。更高的功率降解伴随着 EVA 交联、乙酸乙烯酯含量、黄度指数的显着增加，以及含有与光热反应降解产物相关的不饱和部分的官能团的存在，以及结晶度的更大降低。密封 G/G 模块中没有聚合物背板，限制了光漂白并增强了挥发性乙酸和其他降解副产物的截留，在导致 G/G 模块中更高的 EVA 降解方面起着重要作用。本文得出的结论是，几十年来，EVA 可能是 G/B 模块密封剂的不错选择，但由于潜在的脱气、腐蚀和/或变色问题，它可能被证明是 G/G 模块的不合适选择。离聚物或基于聚酯的密封剂（如聚烯烃）可能最适合 G/G 模块，因为它似乎是当前行业的趋势。